In oil fields, there are many instances in which crude oil does not flow freely under its own pressure from wells. In such cases, artificial "lift" methods utilize a reciprocating polished rod with a plunger down-hole to move the fluid out of the ground and into storage tanks. The equipment (pump unit) which drives the reciprocating rod takes on various forms, the most widely used is a pump jack. A seal system called a stuffing box is used to prevent fluid leakage at the point where the rod enters the ground.
Many known seal units rely upon the contained well fluid to provide both cooling and lubrication for the stuffing box. However, well fluids are often produced at high temperatures or with entrained abrasive material. In some wells, the produced fluid is extremely corrosive. Such adverse conditions sometimes require frequent replacement of the fluid seals.
Furthermore, the movement of the surface pumping unit or misalignment of the rod can tend to cause the reciprocating polished rod to be moved out of longitudinal alignment with the seals, thereby causing uneven wear and premature seal failure. It is therefore important to maintain the polished rod in concentric longitudinal alignment with the seals contained in the stuffing box.